The present invention relates to magnetic recording technology, and more particularly to a tunneling magnetoresistive read head which is capable of being used in high density magnetic recording and can be easily manufactured.
Recently, tunneling magnetoresistive (xe2x80x9cTMRxe2x80x9d) junctions have become of interest for potential use in reading recording media in a magnetoresistive (xe2x80x9cMRxe2x80x9d) head. FIG. 1 is a diagram of a conventional TMR junction 10. Also depicted in FIG. 1 are leads 11 and 19. Not depicted are conventional shields and gaps which would surround the conventional TMR junction 10 if the TMR junction 10 is used as a sensor. The conventional TMR junction 10 includes a conventional antiferromagnetic (xe2x80x9cAFMxe2x80x9d) layer 12, a conventional pinned layer 14, a conventional insulating spacer layer 16 and a conventional free layer 18. The conventional pinned layer 14 and conventional free layer 18 are ferromagnetic. The conventional pinned layer 14 has its magnetization fixed, or pinned, in place because the conventional pinned layer 14 is magnetically coupled to the conventional AFM layer 12. The magnetization of the conventional free layer 18 may be free to rotate in response to an external magnetic field. The conventional pinned layer 14 is typically composed of Co, Fe, or Ni. The conventional free layer 18 is typically composed of Co, Co90Fe10, or a bilayer of Co90Fe10 and permalloy. The conventional insulating spacer layer 16 is typically composed of aluminum oxide (Al2O3).
For the conventional TMR junction 10 to function, current is driven between the leads 11 and 19, perpendicular to the plane of the layers 12, 14, 16 and 18 of the conventional TMR junction 10. The MR effect in the conventional TMR junction 10 is believed to be due to spin polarized tunneling of electrons between the conventional free layer 18 and the conventional pinned layer 14. When the magnetization of the conventional free layer 18 is parallel or antiparallel to the magnetization of the conventional pinned layer 14, the resistance of the conventional TMR junction 10 is minimized or maximized. When the magnetization of the conventional free layer 18 is perpendicular to the magnetization of the conventional pinned layer 14, the bias point for the TMR junction 10 is set. The magnetoresistance, MR, of a MR sensor is the difference between the maximum and minimum resistances of the MR sensor. The MR ratio of the MR sensor is typically called xcex94R/R, and is typically given as a percent. The intrinsic magnetoresistance of such a conventional TMR junction 10 is approximately seventeen percent.
TMR junctions, such as the conventional TMR junction 10, are of interest for MR sensors for high density recording applications. Currently, higher recording densities, for example over 40 gigabits (xe2x80x9cGbxe2x80x9d) per square inch, are desired. When the recording density increases, the size of and magnetic field due to the bits decrease. Consequently, the bits provide a lower signal to a read sensor. In order to maintain a sufficiently high signal within a MR read head, the signal from the read sensor for a given magnetic field is desired to be increased. One mechanism for increasing this signal would be to use an MR sensor having an increased MR ratio.
Although the conventional TMR junction 10 is approximately seventeen percent, a higher MR ratio is desired. Some conventional TMR junctions 10 have an increased MR ratio due to the resistance effect of the leads 11 and 19. In such conventional TMR junctions 10, an MR ratio of up to forty percent has been reported. However, the high MR ratio for such conventional TMR junctions 10 is due to lead resistance. The resistance of the leads 11 and 19 is much higher than the resistance of the conventional TMR junction itself of the conventional TMR sensor 10, which is on the order of sixty ohms per micrometer squared. Consequently, the resistance of the combination of the TMR junction 10 and the leads 11 and 19 is high.
One of ordinary skill in the art will readily realize that a high resistance for the conventional TMR sensor 10 and leads 11 and 19 results in a slow response. Because the combination of the conventional TMR junction 10 and leads 11 and 19 have a high resistance, the time constant for the combination is large. As a result, the response time for the conventional TMR junction 10 is long. The large response time results in a low data transfer rate, which is undesirable.
FIG. 2A depicts another conventional TMR junction 20 disclosed in xe2x80x9cInverse Tunnel Magnetoresistance in Co/SrTiO3/La0.7Sr0.3MnO3: New Ideas on Spin-Polarized Tunnelingxe2x80x9d J. M. De Teresa, A. Barthelemy, A. Fert, J. P. Contour, R. Lyonnet, F. Montaigne, P. Seneor, and A. Vaures, Phys. Rev. Lett., Vol. 82, No. 21, 4288-4291 (1999). Also depicted in FIG. 1B are leads 21 and 29, which are used to carry current to and from the conventional TRM junction 20. The conventional TMR sensor 20 includes an antiferromagnetic layer 22. Above the antiferromagnetic layer is a conventional La0.7Sr0.3MnO3 (LSMO) pinned layer 24. Above the LSMO pinned layer 24 is a SrTiO3 (STO) insulating layer 26. On the side of the STO insulating layer 26 is a conventional free layer 28 composed of Co or LSMO. The MR ratio of the conventional TMR junction 20 is higher than that of the conventional TMR junction 10.
FIG. 2B depicts a conventional method 40 for forming the conventional TMR junction 20. The LSMO pinned layer 24 is provided using pulsed laser deposition at seven hundred degrees Celsius and an oxygen pressure of three hundred and fifty millitorr, via step 42. The STO insulating layer 26 is then provided using pulsed laser deposition at seven hundred degrees Celsius and an oxygen pressure of three hundred and fifty millitorr, via step 44. The conventional pinned layer 28 of Co is then provided using molecular beam epitaxy or sputtering, via step 46.
Referring to FIGS. 2A and 2B, the conventional TMR junction 20 utilizes the STO insulating layer 26 in order to improve the MR for the conventional TMR junction 20. It is believed that d-shell electrons can tunnel more readily through the STO insulating layer 26 than through an insulating layer such as the aluminum oxide insulating spacer layer 16 used in the conventional TMR junction 10. Ferromagnetic materials, such as Co, have d-shell electrons in their unfilled shell. Moreover, the magnetic properties of many ferromagnetic materials are dominated by the d-shell electrons. The STO insulating layer 26 more readily forms d electron bonds with the conventional free layer 28 at the interface between the STO insulating layer 26 and the conventional free layer 28. As a result, it is believed that the d-shell electrons from the conventional free layer 28 can more readily tunnel through the STO insulating layer 26. The same is true for the STO insulating layer 26 and the conventional LSMO pinned layer 24. As a result, tunneling of spin polarized electrons is more likely to take place in the conventional TMR junction 20 than in the conventional TMR junction 10, which has an insulating spacer layer 16 of aluminum oxide through which s-shell electrons are more likely to tunnel. Therefore, the MR ratio of the conventional TMR junction 20 is higher.
In addition, the LSMO pinned layer 24 is what is known as a half metallic ferromagnet. A half metallic ferromagnet has electrons of only one spin type in its unfilled shells. The spin polarization of a material is proportional to the number of spin up electrons in the material""s unfilled shell minus the number of spin down electrons in the material""s unfilled shell. The spin polarization is typically expressed as a percentage. Thus, a half metallic ferromagnet has a spin polarization of one hundred percent. It has been postulated that the MR ratio for a TMR junction is 2*P1*P2/(1+P1*P2), where P1and P2 are the spin polarizations of the free layer and the pinned layer, respectively. For the TMR junction 20, the MR ratio is increased because P2 is one hundred percent (or one, expressed as a fraction). As a result, the MR ratio for the conventional TMR junction 20 is increased, and has been observed to reach approximately fifty percent.
Although the conventional TMR junction 20 has improved MR, one of ordinary skill in the art will readily realize that the TMR junction 20 may not be suitable for use as a sensor in a MR head. In particular, the TMR junction 20 is formed using very high temperature and energy deposition techniques for both the LSMO pinned layer 24 and the STO insulating spacer layer 26. As a result, the TMR junction 20 itself and other structures which may be used in a MR head, such as shields or leads, may be damaged. As a result, the performance of the TMR junction 20 is adversely affected. Because the LSMO pinned layer 24 is deposited using high temperature laser ablation, the conventional AFM layer 22 may be heated during deposition of the LSMO pinned layer 24. Heating of the AFM layer 22 may change the crystal structure of the AFM layer 22, thereby changing the magnetic properties of the AFM layer 22. Consequently, the AFM layer 22 will be less able to pin the magnetization of the LSMO pinned layer 24 in the desired direction. The TMR junction 20 may not, therefore, function as desired. Furthermore, other structures such as the shields or (not shown in FIGS. 1, 2A or 2B) or lead 21 may be damaged by heating during deposition of the LSMO pinned layer 24 or the STO insulating layer 26. If the shields are damaged, the shields may not adequately perform their desired function, screening the TMR junction 20 from the magnetic due to bits which are not being read. As a result, the TMR junction 20 may read spurious magnetic fields as part of the magnetic field of the bit desired to be read. Performance of the TMR junction 20 may, therefore, be adversely affected because of the deposition of the LSMO pinned layer 24 and, to a lesser extent, the deposition of the STO insulating layer 26.
Accordingly, what is needed is a system and method for providing a TMR sensor which is capable of reading information stored on magnetic recording media at higher densities and which can be fabricated without adversely affecting the performance of the TMR sensor. The present invention addresses such a need.
The present invention provides a method and system for providing a magnetoresistive sensor that reads data from a recording media. The method and system comprise providing an antiferromagnetic layer, providing a pinned layer without adversely affecting performance of the magnetoresistance sensor, providing a free layer, and providing an insulating spacer layer disposed between the pinned layer and the free layer. The pinned layer is magnetically coupled to the antiferromagnetic layer. The pinned layer is also a half metallic ferromagnet. The free layer is magnetic. The insulating spacer layer is sufficiently thin to allow tunneling of charge carriers between the pinned layer and the free layer. Furthermore, the insulating spacer layer allows for d-bonding between a portion of the free layer and a portion of the insulating spacer layer.
According to the system and method disclosed herein, the present invention provides a tunneling magnetoresistive sensor which has a high magnetoresistance and which can be fabricated using techniques which will not adversely affect the performance of the magnetoresistive sensor. Consequently, the MR head is capable of reading higher density recording media and fabricated using techniques similar to those currently used for conventional magnetoresistive heads.